This invention relates to compounds and compositions comprising specific metal salts of hexahydrophthalic acid (hereinafter HHPA) in order to provide highly desirable properties within thermoplastic articles. The inventive HHPA derivatives are useful as nucleating and/or clarifying agents for such thermoplastics, and are practical to produce and handle. Such compounds provide excellent crystallization temperatures, stiffness, and acid scavenger compatibility within target polyolefins. Also, such compounds exhibit very low hygroscopicity and therefore excellent shelf stability as powdered or granular formulations. Thermoplastic additive compositions and methods of producing polymers with such compounds are also contemplated within this invention.
All U.S. patents cited below are herein fully incorporated by reference.
As used herein, the term xe2x80x9cthermoplasticxe2x80x9d is intended to mean a polymeric material that will melt upon exposure to sufficient heat but will retain its solidified state, but not prior shape without use of a mold or like article, upon sufficient cooling. Specifically, as well, such a term is intended solely to encompass polymers meeting such a broad definition that also exhibit either crystalline or semi-crystalline morphology upon cooling after melt-formation. Particular types of polymers contemplated within such a definition include, without limitation, polyolefins (such as polyethylene, polypropylene, polybutylene, and any combination thereof), polyamides (such as nylon), polyurethanes, polyesters (such as polyethylene terephthalate), and the like (as well as any combinations thereof).
Thermoplastics have been utilized in a variety of end-use applications, including storage containers, medical devices, food packages, plastic tubes and pipes, shelving units, and the like. Such base compositions, however, must exhibit certain physical characteristics in order to permit widespread use. Specifically within polyolefins, for example, uniformity in arrangement of crystals upon crystallization is a necessity to provide an effective, durable, and versatile polyolefin article. In order to achieve such desirable physical properties, it has been known that certain compounds and compositions provide nucleation sites for polyolefin crystal growth during molding or fabrication. Generally, compositions containing such nucleating compounds crystallize at a much faster rate than unnucleated polyolefin. Such crystallization at higher temperatures results in reduced fabrication cycle times and a variety of improvements in physical properties, such as, as one example, stiffness.
Such compounds and compositions that provide faster and/or higher polymer crystallization temperatures are thus popularly known as nucleators. Such compounds are, as their name suggests, utilized to provide nucleation sites for crystal growth during cooling of a thermoplastic molten formulation. Generally, the presence of such nucleation sites results in a larger number of smaller crystals. As a result of the smaller crystals formed therein, clarification of the target thermoplastic may also be achieved, although excellent clarity is not always a result. The more uniform, and preferably smaller, the crystal size, the less light is scattered. In such a manner, the clarity of the thermoplastic article itself can be improved. Thus, thermoplastic nucleator compounds are very important to the thermoplastic industry in order to provide enhanced clarity, physical properties and/or faster processing.
As an example, dibenzylidene sorbitol derivatives are common nucleator compounds, particularly for polypropylene end-products. Compounds such as 1,3-O-2,4-bis(3,4-dimethylbenzylidene) sorbitol (hereinafter DMDBS), available from Milliken Chemical under the trade name Millad(copyright) 3988, provide excellent nucleation and clarification characteristics for target polypropylenes and other polyolefins. Other well known nucleator compounds include sodium benzoate, sodium 2,2xe2x80x2-methylene-bis-(4,6-di-tert-butylphenyl) phosphate (from Asahi Denka Kogyo K.K., known as NA-11), aluminum bis[2,2xe2x80x2-methylene-bis-(4,6-di-tert-butylphenyl)phosphate] (also from Asahi Denka Kogyo K.K., known as NA-21), talc, and the like. Such compounds all impart high polyolefin crystallization temperatures; however, each also exhibits its own drawback for large-scale industrial applications.
For example, of great interest is the compatibility of such compounds with different additives widely used within typical polyolefin (e.g., polypropylene, polyethylene, and the like) plastic articles. For instance, calcium stearate is a very popular acid neutralizer present within typical polypropylene formulations to protect the stabilizing additives (such as light stabilizers, antioxidants, etc.) from catalyst residue attack. Unfortunately, most of the nucleator compounds noted above also exhibit deleterious reactions with calcium stearate within polyolefin articles. For sodium, and other like metal ions, it appears that the calcium ion from the stearate transfers positions with the sodium ions of the nucleating agents, rendering the nucleating agents ineffective for their intended function. As a result, such compounds sometimes exhibit unwanted plate-out characteristics and overall reduced nucleation performance (as measured, for example, by a decrease in crystallization temperature during and after polyolefin processing). Other processing problems are evident with such compounds as well.
Other problems encountered with the standard nucleators noted above include inconsistent nucleation due to dispersion problems, resulting in stiffness and impact variation in the polyolefin article. Substantial uniformity in polyolefin production is highly desirable because it results in relatively uniform finished polyolefin articles. If the resultant article does not contain a well-dispersed nucleating agent, the entire article itself may suffer from a lack of rigidity and low impact strength.
Furthermore, storage stability of nucleator compounds and compositions is another potential problem with thermoplastic nucleators and thus is of enormous importance as well. Since nucleator compounds are generally provided in powder or granular form to the polyolefin manufacturer, and since uniform small particles of nucleating agents is imperative to provide the requisite uniform dispersion and performance, such compounds must remain as small particles through storage. Certain nucleators, such as sodium benzoate, exhibit high degrees of hygroscopicity such that the powders made therefrom hydrate easily resulting in particulate agglomeration. Such agglomerated particles may require further milling or other processing for deagglomeration in order to achieve the desired uniform dispersion within the target thermoplastic. Furthermore, such unwanted agglomeration due to hydration may also cause feeding and/or handling problems for the user.
These noticeable problems have thus created a long-felt need in the thermoplastic industry to provide nucleating/clarifying agents that do not exhibit the aforementioned problems and provide excellent peak crystallization temperatures for the target thermoplastics themselves, particularly with a wide variety of typical and necessary acid scavenger additives. To date, the best compounds for this purpose remain those noted above. Unfortunately, nucleators exhibiting exceptionally high peak crystallization temperatures, low hygroscopicity properties, excellent dispersion and concomitant clarity and stiffness, as well as compatibility with most standard polyolefin additives (such as, most importantly, calcium organic salt acid scavengers) have not been accorded the different thermoplastic industries. Such problems are not limited to polyolefins and are common within all thermoplastic applications in which nucleating agents are used.
Therefore, an object of the invention is to provide a nucleator compound and compositions thereof that exhibit excellent calcium stearate compatibility within target thermoplastic articles and formulations. A further object of the invention is to provide a thermoplastic nucleating agent that provides excellent high peak crystallization temperatures, for example, to polypropylene articles and formulations, and also exhibits extremely low hygroscopicity in order to accord an extremely good shelf-stable additive composition. Another object of the invention is to provide an easily dispersed nucleator compound such that said polyolefin exhibits very high stiffness and good clarity. Additionally, it is an object of this invention to provide a nucleator compound or composition which may be used in various thermoplastic media for myriad end-uses.
Accordingly, this invention encompasses metal salts of a compound conforming to Formula (I) 
wherein M1 and M2 are the same or different and are selected from at least one metal cation of calcium, strontium, lithium, and monobasic aluminum, and wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are either the same or different and are individually selected from the group consisting of hydrogen, C1-C9 alkyl [wherein any two vicinal (neighboring) or geminal (same carbon) alkyl groups may be combined to form a carbocyclic ring of up to six carbon atoms], hydroxy, C1-C9 alkoxy, C1-C9 alkyleneoxy, amine, and C1-C9 alkylamine, halogens (fluorine, chlorine, bromine, and iodine), and phenyl. The term xe2x80x9cmonobasic aluminumxe2x80x9d is well known and is intended to encompass an aluminum hydroxide group as a single cation bonded with the two carboxylic acid moieties. Furthermore, form each of these potential salts, the stereochemistry at the asymmetric carbon atoms may be cis or trans, although cis is preferred.
As noted above, in order to develop a proper thermoplastic nucleator for industrial applications, a number of important criteria needed to be met. The inventive calcium, strontium, monobasic aluminum, and lithium HHPA salts meet all of these important requirements very well. For instance, these inventive compounds do not hydrate readily and thus granular or powder formulations of such a salt do not agglomerate or clump together. The cost benefits from such shelf stability are apparent since there is little if any need to separate agglomerated powders upon introduction to thermoplastic processing equipment. Furthermore, as discussed in greater detail below, these inventive salts provide excellent high peak crystallization temperatures in a variety of polyolefin and polyester formulations, particularly within random copolymer polypropylene (hereinafter RCP), homopolymer polypropylene (hereinafter HP), impact copolymer polypropylene (hereinafter ICP), syndiotactic polypropylene (s-PP), polyethylene terephthalate (hereinafter PET), polyamides (such as nylons), and any combinations thereof. Additionally, such inventive salts provide high stiffness (modulus) characteristics to the overall final polyolefin product without the need for extra fillers and reinforcing agents. Lastly, and of great importance within the polypropylene industry, such inventive salts do not react deleteriously with calcium stearate co-additives. Such a property, combined with the other attributes, is highly unexpected and unpredictable.
Such inventive compounds thus provide excellent nucleating capability. Sodium salts of certain aromatic and cycloaliphatic carboxylic acids have been discussed within the prior art, most notably within U.S. Pat. No. 3,207,739 to Wales. Broadly disclosed, the patentee includes metal salts of a number of such compounds, most particularly sodium, although Group I and II metals are also broadly discussed. However, patentee specifically states that aromatic benzoates, in particular sodium benzoate, are the best compounds for polyolefin nucleation purposes. Furthermore, patentee mentions strontium as a cation for benzoate alone and specifically teaches away from the utilization of calcium salts due to heat processing problems. Additionally, patentee equates Group I and II metals as cations for his preferred benzoates; however, as discussed below in greater detail, it is evident that other Group II metals, such as magnesium and barium, are highly ineffective with HHPA as polyolefin nucleators. Lastly, it has now been found that in comparison with patentee""s decidedly preferred sodium benzoate, the inventive compounds provide more beneficial properties, including, without limitation, less susceptibility to plate-out and blooming on the mold during polyolefin article formation, lower hygroscopicity, and again of greater importance, less reactivity with calcium stearate thereby permitting greater amounts of both compounds to function in their intended capacities within the target polyolefin formulation.
The inventive HHPA salts are thus added within the target thermoplastic in an amount from about 0.01 percent to 2.0 percent by weight, more preferably from about 0.2 to about 1.5 percent, and most preferably from about 0.05 to 1.0 percent, in order to provide the aforementioned beneficial characteristics. It may also be desirable to include up to 50% or more of the active compound in a masterbatch, although this is not a restriction. Optional additives within the inventive HHPA salt-containing composition, or within the final thermoplastic article made therewith, may include plasticizers, stabilizers, ultraviolet absorbers, and other similar standard thermoplastic additives. Other additives may also be present within this composition, most notably antioxidants, antimicrobial agents (such as silver-based compounds, preferably ion-exchange compounds such as ALPHASAN(copyright) antimicrobials from Milliken and Company), antistatic compounds, perfumes, chlorine scavengers, and the like. These coadditives, along with the nucleating agents, may be present as an admixture in powder, liquid, or in compressed/pelletized form for easy feeding. The use of dispersing aids may be desirable, such as polyolefin (e.g., polyethylene) waxes, stearate esters of glycerin, montan waxes, and mineral oil. Basically, the inventive metal HHPA compounds may be present (up to 20% by weight or more) in any type of standard thermoplastic (e.g., polyolefin, most preferably) additive form, including, without limitation, powder, prill, agglomerate, liquid suspension, and the like, particularly comprising the dispersing aids described above. Compositions made from blending, agglomeration, compaction, and/or extrusion may also be desirable.
The term polyolefin or polyolefin resin is intended to encompass any materials comprised of at least one semicrystalline polyolefin. Preferred examples include isotactic and syndiotactic polypropylene, polyethylene, poly(4-methyl)pentene, polybutylene, and any blends or copolymers thereof, whether high or low density in composition. The polyolefin polymers of the present invention may include aliphatic polyolefins and copolymers made from at least one aliphatic olefin and one or more ethylenically unsaturated co-monomers. Generally, the co-monomers, if present, will be provided in a minor amount, e.g., about 10 percent or less or even about 5 percent or less, based upon the weight of the polyolefin. Such comonomers may serve to assist in clarity improvement of the polyolefin, or they may function to improve other properties of the polymer. Higher amounts of co-monomer (for instance, ethylene, e.g., 10-25% or more), may also be present in the polyolefin to engender greater impact resistance (hereinafter impact copolymer, or ICP""s). Other polymers or rubber (such as EPDM or EPR) may also be compounded with the polyolefin. Other co-monomer examples include acrylic acid and vinyl acetate, etc. Examples of olefin polymers whose transparency and crystallization temperature can be improved conveniently according to the present invention are polymers and copolymers of aliphatic mono-olefins containing 2 to about 6 carbon atoms which have an average molecular weight of from about 10,000 to about 2,000,000, preferably from about 30,000 to about 300,000, such as, without limitation, polyethylene (PE), linear low density polyethylene (LLDPE), isotactic polypropylene (I-PP), syndiotactic polypropylene (s-PP), random copolymer polypropylene (RCP), crystalline ethylenepropylene copolymer (ICP), poly(1-butene), poly(4-methylpentene), poly(1-hexene), poly(1-octene), and poly(vinyl cyclohexene). The polyolefins of the present invention may be described as basically linear, regular polymers that may optionally contain side chains such as are found, for instance, in conventional, low density polyethylene. Although polyolefins are preferred, the nucleating agents of the present invention are not restricted to polyolefins, and may also give beneficial nucleation properties to polymers such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), as well as polyamides such as Nylon 6, Nylon 6,6, and others. Generally, any thermoplastic composition having some degree of crystalline content may be improved with the nucleating agents of the present invention.
The compositions of the present invention may be obtained by adding the inventive HHPA salt (or combination of salts or composition comprising such salts) to the thermoplastic polymer or copolymer and merely mixing the resultant composition by any suitable means. The composition may then be processed and fabricated by any number of different techniques, including, without limitation, injection molding, injection blow molding, injection stretch blow molding, injection rotational molding, extrusion, extrusion blow molding, sheet extrusion, film extrusion, cast film extrusion, foam extrusion, thermoforming (such as into films, blown-films, biaxially oriented films), thin wall injection molding, and the like into a fabricated article.
The nucleated thermoplastic is intended to be utilized as, for instance and not by limitation, medical devices, such as pre-filled syringes for retort applications, intravenous supply containers, and blood collection apparati; food packages; liquid containers, such as for drinks, medicines, shampoos, and the like; apparel cases; microwaveable articles; shelves; cabinet doors; mechanical parts; automobile parts; sheet; pipes and tubes; rotationally molded products; blow-molded products; fiber (spun or nonwoven); compression molded products; basically any thermoplastic article wherein the effects of nucleation may be advantageous.
Examples of the particularly preferred metal salts of HHPA within the scope of the present invention and compositions thereof are presented below.
Production of Inventive HHPA Salts